Vitamin A Properties
- Other names: Beta carotene, retinol
- Chemical formula: C20H30O
- Fat or water soluble? Fat soluble
- Forms: Carotenoids (plant form), retinol (form used in the body), and various related forms such as retinoic acid, retinal, retinyl esters
- Recommended daily intake: Since vitamin A comes in so many different forms, it is measured in units called RAE, or Retinol Activity Equivalents. One RAE is equivalent to 1/1000 mg (1 μg) of retinol. The recommended daily intake of vitamin A for average adults is is 700 RAE for women and 900 RAE for men.
Roles in the Body
- Necessary for good vision. The name “retinol” comes from the word retina, the part of the eye that forms images. Vitamin A helps prevent macular degeneration, which can lead to blindness.
- Antioxidant. Vitamin A neutralizes “free radicals” which can damage cells and cause cancer.
- Immune function. Vitamin A helps protect against infection both by promoting proper immune system function, by keeping the skin healthy (the skin keeps infectious organisms out), and by maintaining the lining of the lungs so it can remove microorganisms.
- New cell growth and differentiation. Differentiation is the process by which new cells specialize into different types such as nerve, bone, or muscle.
- Protects against some common effects of aging, such as arthritis, wrinkles and age spots.
Vitamin A Deficiency
Symptoms of vitamin A deficiency include night blindness, which can lead to permanent blindness in severe cases; increased susceptibility to infection; and skin problems. Vitamin A deficiency is common in developing nations but rare in developed countries. Those most susceptible in developed countries include those on strict diets and those who abuse alcohol. Alcohol abuse presents a one-two punch: alcohol depletes vitamin A stores, and alcoholics often have poor diets. Chronic diarrhea, iron deficiency, and any condition that interferes with nutrient absorption in general can lead to Vitamin A deficiency.
Vitamin A Overdose (Hypervitaminosis A)
An excess of vitamin A can lead to liver problems, central nervous system disorders, and decreased bone density, and can also cause birth defects. It is impossible to overdose on vitamin A through consumption of plant products because the carotenoids in plants are an inactive form. The skin may turn orange due to storage of carotene by the body. Consumption of excessive amounts of liver, which contains large amounts of retinol, and of supplements can lead to overdose symptoms.
Food Sources of Vitamin A
Liver is the most concentrated food source of vitamin A. Carrots and sweet potatoes are very high in beta carotene, and a single carrot exceeds the recommended minimum daily intake. Other foods that contain significantly less of the vitamin but that are nonetheless rich sources include kale, mangoes, spinach, papaya, red peppers, apricots, and cantaloupe. Since beta carotene is a yellow-orange pigment, it may be easy to remember that most foods this color (but not oranges) are high in beta carotene, as are dark green vegetables. Eggs and dairy products also contain vitamin A.
- Dietary Supplement Fact Sheet: Vitamin A and Carotenoids. National Institutes of Health.
- Vitamin A (Retinol). Ohio State University.